Resist materials used for etching, plating and the like in the field of manufacturing conventional printed circuit boards include widely employed photosensitive resin compositions and photosensitive elements obtained by laminating these onto supports and coating them with protective films.
When a photosensitive element is used for manufacture of a printed circuit board, first the photosensitive element is laminated onto a circuit-forming board such as a copper base and subjected to pattern exposure through a mask film or the like, after which the unexposed sections of the photosensitive element are removed with a developing solution to form a resist pattern. Next, the resist pattern is used as a mask for etching or plating of the circuit-forming board on which the resist pattern has been formed, in order to form a circuit pattern, and finally the cured sections of the photosensitive element are released and removed from the board to obtain a printed circuit board.
Recently, such printed circuit board manufacturing methods are implementing laser direct writing, whereby active light rays are directly irradiated as an image using digital data, without a mask film. YAG lasers, semiconductor lasers and the like are used as light sources for direct writing methods for their safety and handleability, and in recent years techniques using high-output gallium nitride-based blue lasers, which have long usable life, have been proposed.
Also recently, the direct writing method known as DLP (Digital Light Processing) exposure has been studied as a laser direct writing method that allows formation of finer patterns than in the past, for the increasingly high definitions and high densities of semiconductor package printed circuit boards. Generally speaking, DLP exposure uses active light rays with a wavelength of 390-430 nm, with a violet semiconductor laser as the light source. For general purpose printed circuit boards there are mainly used exposure methods that employ polygon multibeams with wavelengths of 355 nm from a YAG laser light source, which are suitable for small-batch, multi-variety products.
Several types of sensitizing agents are used in photosensitive resin compositions to match the different wavelengths of light sources in laser direct writing methods (see Patent documents 1 and 2, for example).